Single wall magnetic domains or magnetic bubbles have been recognized for a number of years and much work appears in the published and patent literature concerning the application of this phenomenon to diverse devices. In a majority of these applications, however, an external magnetic fieid is required to stably support the single wall domains or magnetic bubbles. In particular, the external magnetic field is required to assure reproducible bubble generation and maintain bubbles of substantially constant size and stability for propagation and sensing purposes. The requirement of this external magnetic field leads to complications in device application since field coils must be provided to generate the magnetic field. The presence of the field coils inhibits the freedom of the designer in laying out the device' structure and adds complications such as a requirement for a power source for the field coil and in some applications even cooling structures for cooling the field coils.
A number of suggestions have been made in the prior art for elimination of the external magnetic field. Typical of these proposals are two Bobeck patents, U.S. Pat. No. 3,529,303 and U.S. Pat. No. 3,714,640; a Copeland Patent, U.S. Pat. No. 3,678,478; and an article entitled "Internal Bias Effect of Double Layer Epitaxial Garnet Films" appearing in IEEE Transactions on Magnetics, Volume MAG-9, No. 3, September 1973, beginning at page 381 by Uchishiba et al.
The solution suggested by Bobeck, however, requires a permanent magnetic material overlying the magnetic film supporting the magnetic domains. This sheet of permanent magnetic material interferes with the operation of domain propagating arrangements and furthermore, it has been found, that the effective field supplied by this arrangement is not sufficient to support optimum sized domains. For efficient utilization, of course, it is desired that the diameter of the domains be as small as possible. Because of the interrelation between material characteristic and film thickness, this generally requires relatively thick film and it has been found with such films that the permanent magnetic layer of Bobeck supplies an inadequte field strength.
The Copeland arrangement requires a plurality of stacked layers of materials in which domains can be moved. Of course, this is entirely inadequate where only a single layer of domains is desired and the multilayer arrangement complicates the interconnection problem.
The Uchishiba article specifies only a few particular combinations of materials in which it has been found that the internal bias is sufficient to support the magnetic domains. The article does not provide a basis for using materials other than those expressly disclosed in the article. In other words there is no teaching of a systematic basis or criteria for selecting appropriate materials and the parameters for a self-biased structure for supporting single wall domains.